1. Field of the Invention
The present invention relates generally to Group III-V lateral injection heterostructure devices, and more particularly, to a lateral p-i-n photodetector having doped self-aligned graded contact diffusion regions of opposite conductivity types which penetrate an abrupt heterojunction formed by the upper two layers and a method for manufacturing same.
2. Description of the Prior Art
For both majority and minority carrier lateral injection heterostructure devices, it is desired to have regions where an abrupt heterojunction is maintained and regions where it is compositionally graded. Examples of devices where this is of use are optical devices such as photodetectors and lasers and electronic devices such as metal-semiconductor field effect transistors, heterostructure metal-semiconductor field effect transistors and heterostructure field effect transistors. In such devices, the abrupt heterojunction is necessary in regions where it is desired to prevent carriers from reaching the surface of the device to reduce the leakage current. The graded region is desired where either injection or collection of carriers is required to occur which is generally associated with doped contact diffusion regions. A graded region is desired in a doped contact diffusion region because it will increase the speed of the device due to carriers being efficiently collected or injected by the graded diffusion regions. In order to fabricate a graded contact diffusion region in such heterostructure devices, the diffusion region must penetrate a type I Group III-V compound semiconductor heterojunction in which the higher bandgap III-V compound semiconductor has its conduction band higher and valence band lower than the corresponding conduction and valence band in the lower bandgap III-V compound semiconductor. Due to a requirement of high carrier lifetimes, small size and high quality ohmic contacts in such devices, ion implantation techniques are not suitable for forming contact regions in Group III-V heterostructure devices. In addition, ion implantation followed by annealing does not lead to grading of heterostructures.
Various ohmic contacts which can be used to form diffusion regions in Group III-V compound semiconductors have been developed. For example, U.S. Pat. No. 4,593,307 is directed to the formation of a molybdenum germanide contact to n-type gallium arsenide. U.S. Pat. No. No. 4,540,446 shows an n-type contact diffusion region formed by ion implantation of an n-type dopant into a germanium film and a subsequent heating step diffuses the dopant into a gallium arsenide substrate. An article by Tiwari, S., et al., entitled "Ohmic Contacts to N-GaAs with Germanide Overlayers", Tech. Dig. of IEDM, 115 (Dec. 1983) shows an ohmic contact to n-GaAs which uses germanium as the diffusing dopant impurity and molybdenum germanide as a contacting metallurgy.
U.S. Pat. No. No. 4,843,033 relates to a method for diffusing zinc into Group III-V heterojunctions having layers of a small bandgap semiconductor material (GaAs) formed over a layer of a larger bandgap semiconductor material (AlGaAs). Zinc tungsten silicide (ZnWSi.sub.2) is used as a contact and dopant source. During a rapid thermal anneal, the zinc is diffused through two layers of doped GaAs to contact an n-doped layer of AlGaAs. Carriers are free to combine at the surface because the wide bandgap material AlGaAs is below the narrow bandgap material GaAs.
Thus, there is a need to develop a lateral injection Group III-V heterostructure having graded contact diffusion regions which penetrate a heterojunction formed by a layer of a high bandgap III-V compound semiconductor overlying a layer of a low bandgap III-V compound semiconductor and a method for manufacturing such heterostructures.